A video posted online by a Nuevo Laredo news organization showed the shooting, but didn’t show any rock throwing. The video shows a Border Patrol air boat cruising slowly along the U.S. side of the Rio Grande while on the Mexican bank children play and adults gawk at the agents. The camera turns away as the shooting starts, then returns to show Arevalo on the ground, a crowd gathered around him. People on the Mexican bank scream and gesture angrily at the boat, which speeds off. [Veronica] Martinez can be heard in the background screaming, “That’s against the law.”

On Monday, [Veronica] Martinez [U.S. citizen residing in Nuevo Laredo] said, a masked agent on the boat pointed his gun at her as soon as she arrived at the river. The shooting didn’t start until several minutes later, she said, when people on the Mexican bank began haranguing the agents as they circled close to the fleeing swimmer. She told the same story as Lam, that the shooting was unprovoked. Afterward, she said, an agent on the U.S. side of the river hopped into the boat, and it sped upstream toward downtown Laredo.

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By the time she realized what happened Monday night, her daughter, Mariana, was covered in blood, Lam said. Then she realized Arévalo was dying.

Guillermo Arévalo Pedroza was on the banks of the Rio Grande with his youngest daughter in his arms when the deadly bullets started flying Monday night, his wife said. Nora Isabel Lam Gallegos said she, Arévalo and their two young daughters had gone to a park on the river for a birthday celebration. She and her daughters’ birthdays fall close together, and they were having a barbecue, Lam said.

Around dusk, a Border Patrol boat appeared near the Parque Vivero, across the river from an undeveloped stretch of land in South Laredo, she said. The two agents were trying to stop a young man who was swimming from the U.S. to Mexico, not an unusual occurrence on this busy stretch of the border. On the Mexican side of the river, Lam and another witness said, partygoers in the crowded park began heckling the agents and telling them they were going to drown the swimmer.

Then the shooting erupted. “Everything was covered in blood,” Lam, 26, said through tears. “He was already dead. So I started screaming ‘They killed him, they killed him, they have killed him’ (The agents) heard that I said that they had killed him, and they left.”

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“If they’re saying we were throwing rocks, that’s a big lie,” [Veronica] Martinez said. “But if we were, it’s not the same thing, a rock and a bullet.”